U.S. patent application number 10/830038 was filed with the patent office on 2005-11-10 for heater with simultaneous hot spot and mechanical intrusion protection.
Invention is credited to Gerrard, Grahame, Kochman, Dmitry, Kochman, Eric.
Application Number | 20050247700 10/830038 |
Document ID | / |
Family ID | 35115273 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050247700 |
Kind Code |
A1 |
Kochman, Eric ; et
al. |
November 10, 2005 |
HEATER WITH SIMULTANEOUS HOT SPOT AND MECHANICAL INTRUSION
PROTECTION
Abstract
An electrical heater utilizes negative temperature coefficient
material (NTC) and current imbalance between live and neutral ends
of the heater to simultaneously protect the heater from the hot
spot and mechanical intrusion into the heating cable. The NTC
layer, separating the heating wire and current leakage conductor,
becomes electrically conductive at the temperatures above
60.degree. C., thus "leaking" the current to earth. The hot spot is
detected by measuring the current imbalance between line and
neutral connections of the heating cable. The mechanical intrusion
into the heater, such as cable or insulation damage, water or sharp
metal object penetration, is also simultaneously measured by the
same current imbalance measuring system such as Ground Fault
Circuit Interrupter (GFCI). The optional return conductor and metal
foil/mesh hot spot detection shields cancel electromagnetic field.
The heater may contain positive temperature coefficient (PTC)
continuous sensor to control the temperature in the heater. Such
PTC sensor can be made of electrically conductive fibers and/or
metal wires.
Inventors: |
Kochman, Eric; (Highland
Park, IL) ; Gerrard, Grahame; (Lancashire, GB)
; Kochman, Dmitry; (Vernon Hills, IL) |
Correspondence
Address: |
Liniak, Berenato & White
Ste. 240
6550 Rock Spring Drive
Bethesda
MD
20817
US
|
Family ID: |
35115273 |
Appl. No.: |
10/830038 |
Filed: |
April 23, 2004 |
Current U.S.
Class: |
219/544 |
Current CPC
Class: |
H05B 2203/019 20130101;
H05B 3/56 20130101 |
Class at
Publication: |
219/544 |
International
Class: |
H05B 003/44 |
Claims
1. A heater having a durable construction for incorporation into a
plurality of articles, said heater comprising: at least one
continuous heating means, at least one continuous current leakage
conductor, at least one continuous NTC sensing means, placed
between, and electrically connected to said heating means and said
current leakage conductor, said NTC sensing means provides current
leakage between said heating means and said current leakage
conductor; at least one controller, for simultaneous protection
from hot spot and mechanical intrusion into said heater, said hot
spot is detected by measuring the imbalance of electrical current
flowing between live and neutral ends of the electrical circuit of
said heating means;
2. A heater as defined in claim 1 further including at least one
insulation means covering at least one side of combination of said
heating means, said NTC sensing means and said current leakage
conductor;
3. A heater as defined in claim 1 wherein said current leakage
conductor is electrically connected to the ground.
4. A heater as defined in claim 1 wherein said current leakage
conductor is electrically connected to one of the current supply
conductors of said controller;
5. A heater as defined in claim 1 further including sensing
means.
6. A heater as defined in claim 5 wherein said sensing means
comprises PTC temperature sensing means with PTC detector.
7. A heater as defined in claim 1 wherein said at least one NTC
sensing means, placed between, and electrically connected to a
return conductor and said current leakage conductor.
8. A heater as defined in claim 1 wherein said heating means
comprise a melting fuse, said melting fuse comprising at least one
electrically conductive textile fiber as a heating means, said at
least one electrically conductive textile fiber melts at a
temperature above 110.degree. C. and below 350.degree. C.
terminating electrical continuity in said heating means and
preventing a fire hazard in said heating cable.
9. A heater as defined by claim 1, further including a visual
indicator warning of hot spot on said controller.
10. The heater as defined by claim 1, further including sound
signal warning of hot spot in said heater.
11. A method of simultaneous protection by a controller from a hot
spot and mechanical intrusion into said heater, recited in claim 1
comprises steps of: leaking of electrical current between said
heating means and said current leakage conductor, through said NTC
sensing means, detecting an imbalance of electrical current flowing
between live and neutral ends of the electrical circuit of said
heating means, terminating of electrical continuity in said heater
upon reaching predetermined current leakage limiting setting.
12. A method of simultaneous protection by a controller as defined
by claim 11, wherein said controller has separate said current
leakage limiting settings for said hot spot and said mechanical
intrusion in said heater.
13. A method of simultaneous protection by a controller as defined
by claim 12, wherein the hot spot current leakage limiting setting
is lower than mechanical intrusion current leakage limiting
setting.
14. A method of simultaneous protection by a controller as defined
by claim 1-1, wherein said heater further comprising PTC
temperature sensing means and PTC detector to control the maximum
heating level in said heater.
15. A method of simultaneous protection by a controller as defined
by claim 11, further including a visual indicator warning of hot
spot on said controller.
16. A method of simultaneous protection by a controller as defined
by claim 11, further including sound signal warning of hot spot in
said heater.
17. A method of simultaneous protection by a controller as defined
by claim 11 wherein said current leakage conductor is electrically
connected to the ground.
18. A method of simultaneous protection by a controller as defined
by claim 11 wherein said current leakage conductor is electrically
connected to one of the current supply conductors of said
controller;
19. A method of simultaneous protection by a controller as defined
by claim 11, wherein said controller comprises ground fault circuit
interrupter.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] This invention relates to a method of hot spot detection and
overheating protection of flexible electrical heaters, which have
strong metal or carbon containing electrical conductors and
insulation with semi-conductive temperature sensitive
properties.
[0003] 2. Description of the Prior Art
[0004] Heating elements have extremely wide applications in
household items, construction, industrial processes, etc. Their
physical characteristics, such as thickness, shape, size, strength,
flexibility and other characteristics affect their usability in
various applications.
[0005] Numerous types of thin and flexible heating elements have
been proposed. For example, U.S. Pat. No. 5,861,610 to John Weiss
describes the heating wire, which is formed with a first conductor
for heat generation and a second conductor for sensing. The first
conductor and a second conductor are wound as coaxial spirals with
an insulation material electrically isolating two conductors. The
two spirals are counter-wound with respect to one another to insure
that the second turns across, albeit on separate planes, several
times per inch. One of the conductors acts as a heater and another
conductor works as a sensing Positive Temperature Coefficient (PTC)
wire with predetermined electrical resistance characteristics. The
described construction results in a temperature sensing system,
which can detect only the average change of resistance in the
sensing wire due to elevation of the temperature in the heated
product. Therefore, in the event of overheating of a very small
surface area (hot spot) of the electric blanket or pad (for
example, several square inches), the sensor may fail to detect a
minor change of electrical resistance (due to operating resistance
tolerance) in the long heating element. In addition, such heating
cable does not have inherent Thermal-Cut-Off (TCO) capabilities in
the event of malfunction of the controller.
[0006] Gerrard (U.S. Pat. No. 6,310,332) describes an elongated
heating element for an electric blanket comprising a first
conductor means to provide heat for the blanket and extending
lengthwise of the element, a second conductor means extending
lengthwise of the element, and a meltdown layer between the first
and second conductor means which is selected, designed and
constructed or otherwise formed so as to display a negative
temperature coefficient (NTC), and including an electronic
controller set to detect a change in the resistance of the meltdown
layer to provide a means of changing the power supply to the first
conductor means (providing heat to the blanket), to prevent
destruction of the melt down layer. The element further includes a
meltdown detection circuit for detecting meltdown of the meltdown
layer and for terminating power to the first conductor means in the
event that the control means fails and the meltdown layer heats up
to a predetermined degree. The disadvantage of this construction is
that the final safety of the blanket relies on a complex
NTC/meltdown detection system located in the controller. In the
event of controller failure, or significant delays in the detection
of the NTC layer meltdown, severe scorching of the heating product
or a fire can occur. The Gerrard heating system always requires
separate sensing PTC wire, attached to the controller to detect
overheating or hot spots. Such passive PTC sensing conductor needs
an additional pair of lead wires going from the heater to the
sensing control system, which increases weight, size and cost of
the heating systems.
[0007] Another disadvantage of Gerrard's invention is that its
control system utilizes a half-wave power cycle for heating and
another half-wave power cycle for meltdown stroke detection in
order to provide proper heating output and meltdown protection.
Therefore, the heating wire has to be twice as thick as systems
utilizing a full-wave power output. This feature becomes especially
challenging for 120V and other lower voltage heating systems,
compared to traditional European 240V systems. Increased thickness
of the heating wire leads to: (a) increased cost of the heating
conductor; (b) increased overall size of the heating element and
(b) increased heating wire susceptibility to breaking due to
reduced flexibility.
[0008] Kochman (U.S. Pat. No. 6,713,733) describes a soft and
flexible heater which utilizes electrically conductive threads or
fibers as heating media. The conductive fibers are encapsulated by
negative temperature coefficient (NTC) material, forming
temperature sensing heating cables. The heater may contain
continuous positive temperature coefficient (PTC) temperature
sensors to precisely control the temperature in the heater. The
disadvantage of this system is that it requires at least two
independent conductors connected to the control system. The first
conductor acts as a heating means and the second conductor acts as
a heat detection conductor. The NTC hot spot detection system
becomes less sensitive with increase of the length of the cable.
The heating means and heat detection conductor require separate
connections by lead wires to the controller. The electronics which
detect overheating use a signal (drop of potential) which transfers
to the electronic controllers through heat sensing conductors. The
addition of heat sensing conductors for signal transfer and the
addition of extra lead wires, results in increased size of the
heating cable and lead wire cord, thereby reducing their
flexibility and increasing their weight and cost.
[0009] The present invention seeks to alleviate the drawbacks of
the prior art and describes the novel method of hot spot detection,
overheat protection and the fabrication of a heater comprising at
least one of the following heating means: metal wires, metal
fibers, metal coated, carbon containing or carbon coated
threads/fibers, which results in a flexible, strong, heating
element core. A preferred embodiment of the invention consists of
utilizing electrically conductive textile threads/fibers having an
inherent Thermal Cut Off (TCO) function to prevent overheating
and/or fire hazard. However, the proposed heaters preferably
contain metal conductors or combination of metal wires and
conductive textile fibers. The system utilizes an NTC sensing layer
for hot spot detection, which does not require having
low-temperature meltdown characteristics. The heaters described in
this invention may also comprise a continuous temperature PTC
sensor to precisely control heating power output in the heating
product. The system comprises a current leakage conductor and an
electronic or electromechanical device for detecting and comparing
the current imbalance in the heater. One of such devices may
contain Ground Fault Circuit Interrupter (GFCI), which is also
commonly known as "Earth Leakage Circuit Breaker" (ELCB)) to detect
current imbalance in the heater due to current leakage through the
NTC sensing layer from the heating means to the current leakage
conductor. Simultaneously, the same GFCI or other current leakage
detecting device can protect the heating cable from mechanical
intrusion in the heating cable. Such mechanical intrusion may be in
the form of moisture (water) penetration, heating element damage or
direct electrical contact between the heating means and the ground
conductor due to metallic intrusion inside the heating cable.
SUMMARY OF THE INVENTION
[0010] A first objective of the invention is to provide a method of
detecting and preventing hot spots. In order to achieve the first
objective at least one negative temperature coefficient (NTC) layer
is attached to the heating means to provide current leakage to (a)
ground/earth conductor or (b) special current leakage conductor,
connected either to live or neutral current supply lead wire. The
ends of the heating means are connected to the current detectors of
GFCI (or ELCB), or other electronic system which detects an
imbalance between the "live" and "neutral" ends of the heating
cable and disconnects electrical continuity in the heating system
at predetermined current limiting settings. It is preferable that
the NTC layer covers the heating means through the entire length of
the heating element. It is also preferable that the ground shield
(such as mesh or foil) and/or ground wire has a sufficient
electrical connection with the NTC layer through the entire length
of the heating cable.
[0011] The second objective of the invention is to provide a
significantly safe and more reliable heater which can function
properly after it has been subjected to folding, kinks, punctures
or crushing. In order to achieve the second objective, the heater
of the present invention may comprise (a) electrically conductive
threads/fibers and/or metal wires or combination thereof, and (b)
multi-layer insulation of the whole heating cable. The electrically
conductive fibers may be comprised of carbon, metal fibers, and/or
textile threads coated with one or combination of the following
materials: metal, carbon and/or electrically conductive ink. The
multi-layer insulation of the electrically conductive
threads/fibers provides increased dielectric properties, preventing
or minimizing current leakage in the event of abuse of the heater.
The insulation means may be applied in the form of encapsulation
(through extrusion process) or lamination with insulating synthetic
materials, having similar or different thermal and mechanical
characteristics.
[0012] The present invention describes a method of hot spot
detection and overheating protection of the heater. It can be
manufactured in various shapes, and it can be designed for a wide
range of parameters, including but not limited to input voltage,
temperature, power density, type of current (AC or DC) and method
of electrical connection (parallel or in series).
[0013] The heater contains current leakage conductor which may have
a shape of a foil, mesh and/or bare wires, which provide current
leakage path to the grounded electrode conductor of the housing
electrical circuit in the event of heating cable damage, moisture
penetration, metal intrusion onto the cable or local overheating of
the NTC sensing layer.
[0014] The NTC sensing layer usually separates the heating means
and/or the return wire from the current leakage conductor, provided
that they have good electrical and mechanical connection.
[0015] The optional electrically conductive textile fibers also act
as a continuous thermal fuse, terminating or reducing electrical
continuity in the heater at the temperatures 110.degree.
C.-350.degree. C. if dictated by the heating element design.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a cross section of a heating cable consisting
of two layers of outer insulation means, current leakage
conductors, heating means covered by NTC sensing material and an
insulated return conductor.
[0017] FIG. 2 shows a cross section of a heating cable consisting
of one layer of outer insulation means, current leakage conductors
in a form of a mesh or foil shield, heating means covered by NTC
sensing material and an insulated return conductor.
[0018] FIG. 3 shows a cross section of a heating cable consisting
of two layers of outer insulation means, current leakage conductor
in a form of a mesh or foil shield and heating means covered by NTC
sensing material.
[0019] FIG. 4A shows a cross section of a heating cable consisting
of one layer of outer insulation means, current leakage conductors
in a form of a mesh or foil shield, heating means covered by NTC
sensing material and insulated PTC temperature sensing means.
[0020] FIG. 4B shows a cross section of a heating cable consisting
of one layer of outer insulation means, current leakage conductors
having a form of bare wire conductor, heating means, covered by NTC
sensing material and insulated PTC temperature sensing means.
[0021] FIG. 5 shows a principal electrical circuit diagram of an
electronic control system and heating cable with a single ended
connection including optional PTC temperature sensing means and PTC
detector.
[0022] FIG. 6 shows a principal electrical circuit diagram of the
electronic control system and heating cable with double ended
connection including optional PTC temperature sensing means and PTC
detector.
[0023] FIG. 7 shows a cross section of a flat heating panel with
heating cables covered by a hot spot detection foil sheet on both
sides of the heater.
[0024] FIG. 8 shows a plan view of a heating pad with heating
cables placed on a foil sheet of current leakage conductor.
[0025] FIG. 9 shows and isometric view of a heating cable with
heating means insulated by NTC layer and connected to current
leakage conductor.
[0026] FIG. 10A shows a principal electrical circuit diagram of the
electronic control system and heating cable without grounding
circuit.
[0027] FIG. 10B shows a principal electrical circuit diagram of the
electronic control system and heating cable without grounding
circuit.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The invention consists of a heating element containing: (a)
at least metal wires or metal/carbon containing textile fibers or
combination thereof as heating means, insulated by at least one
layer of NTC sensing means, (b) current leakage conductor,
electrically connected with NTC sensing means and (b) at least one
outer insulation of the heater. The invention describes a method of
hot spot detection and overheating protection, using a combination
of heating means, NTC layer, current leakage conductor and
electronic controller, which detects the current imbalance between
the live end and the neutral end of the heater.
[0029] The term "conductive means" or "conductor" described in this
invention shall mean at least one of the following electrically
conductive materials: metal wires, metal mesh or metal foil,
electrically conductive textile fibers, electricaly conductive
polymers and other conductive materials, suitable for the purpose
of this invention.
[0030] The term "heating means" described in this invention shall
mean electrical conductor, which is used for heat radiation or
current return from live to neutral connections, upon application
of predetermined voltage to the heater. As an example, the
electrically conductive textile fibers, or metal wires or
combination thereof may be considered as heating means. The return
conductor, applied in some embodiments of the invention is also
considered a heating means.
[0031] The term "return conductor" described in this invention
shall mean a second heating means which may be placed inside the
heating cable and connected (bridged) with the first insulated
heating means at one end of the heating cable. Usually the return
conductor is encapsulated by insulation means or by NTC sensing
means in the same manner as the first heating means. Therefore, in
some embodiments of the invention, the return conductor alone may
provide the NTC current leakage for hot spot detection.
[0032] The term "heating cable" or "temperature sensing heating
cable" described in this invention shall mean a heater, or portion
thereof, which contains at least one of the following components:
heating means, sensing means, current leakage conductor and outer
insulation. The heating cable may also contain at least one of the
following sensing means: (a) NTC sensing means, or (b) PTC
temperature sensing means. Usually the heating cable comprises
heating means encapsulated by NTC sensing means, which has good
electrical and mechanical connection with the current leakage
conductor. The heating cable has at least one layer of the outer
insulation means, which insulates all electrical conductors
including the heating means, NTC and/or PTC temperature sensing
means and the current leakage conductor.
[0033] The term "heating cable with double ended connection"
described in this invention shall mean a heating cable which has
electrical termination at the opposite ends of the heating cable.
The current in the heating cable with double ended connection flows
only in one direction at the same time.
[0034] The term "heating cable with single ended connection"
described in this invention shall mean a heating cable which has at
least one insulated heating means and at least one insulated return
conductor. The current in the first heating means and second
heating means (or return conductor) flows in the opposite
directions at the same time, which completely cancels or
significantly reduces electromagnetic field. The heating cable with
single ended connection is powered from one end of the heating
cable and electrically bridged (interconnected) at the opposite end
of the heating cable. It is preferable that the heating and/or
return conductors inside the heating cable are twisted against each
other to reduce electromagnetic field.
[0035] The term "controller" or "electronic controller" described
in this invention shall mean an electronic (solid state) or
electromechanical power control device, which provides sensing,
variation and/or termination of heat radiation in the heater.
Usually, the controller is located between the electrical power
source and the heating means. However, it also may be designed as a
wireless remote controller with the receiver/regulator located
between the electrical power source and the heater.
[0036] The controller of this invention is capable of comparing an
imbalance of current at two (live and neutral) ends of the
electrical circuit of the heating cable. It may have a special
electronic device to detect the current imbalance in the systems
where earth/grounding connection is not available or not required.
Alternatively, it may have a device commonly called Ground Fault
Circuit Interrupter (GFCI) or Earth Leakage Circuit Breaker (ELCB),
which can detect such current imbalance and terminate electrical
continuity at a predetermined current leakage limiting setting in
the heaters with ground connection. It is preferable, that current
leakage setting has a limiting value ranging from 0.1 mA to 100 mA,
depending on application of the heater.
[0037] The term "NTC sensing means" or "NTC sensing layer"
described in this invention shall mean a layer of polymer material
possessing negative temperature coefficient (NTC) characteristics.
The NTC capability of plastic may depend on the use or design of a
single material, or alternatively, the respective quality may be
obtained by coating, cross linking, doping, or mixing of several
materials to achieve the required NTC performance. As an example,
polymers, comprising polyethylene, polyvinyl chloride (PVC),
thermoplastic rubber or polyamide may have NTC sensing
properties.
[0038] For purposes of the invention, the NTC sensing means
exhibits NTC characteristics, preferably in such a way that with
gradual increase of the temperature (for example up to
60-70.degree. C.), its electrical resistance remains almost
unchanged (i.e. it acts as insulation material), but at a certain
predetermined temperature it decreases abruptly. Such an abrupt
fall of electrical resistance is easily detected by a special
control circuit of the controller. It is preferable that the abrupt
decrease in electrical resistance of the NTC sensing means
occurred, somewhere between 60.degree. C. and 130.degree. C., which
will be considered as hot spot limiting temperatures for the
purposes of this invention.
[0039] The term "insulation means" or "nonconductive means"
described in this invention shall mean a layer of nonconductive
material, which insulates conductive means. Such insulation means
may be in the form of extruded or jacketed polymer, thermoplastic
or textile sheet, sleeve, or strip of nonconductive means. As an
example, the insulation means may comprise at least one of the
following polymers: polyvinyl chloride (PVC), silicon rubber,
polyethylene, polypropylene, polyurethane, nylon, polyester,
cross-linked polyethylene and PVC, or other appropriate electrical
insulating materials. The insulation means may also be utilized as
the NTC sensing means in the same heater, depending on the heating
element design and its operation temperature.
[0040] The term "heater" described in this invention shall mean any
electrical heat radiating device which may comprise at least one of
the following components: heating means, sensing means, NTC sensing
means, current leakage conductor, insulation means, and/or
conductor. The heater may have a shape of: (a) round or flat cable,
(b) tape, (c) sheet or (d) sleeve. The heater may include a
temperature sensing and/or temperature limiting electronic or
electromechanical controller.
[0041] The term "metal fibers" shall mean metal fibers/filaments,
having a denier size of synthetic textile fibers. The diameter of
each metal fiber is smaller than the lowest commercially available
metal wire Gauge. An example of metal fibers may be Bekinox.RTM.
stainless steel continuous filament/fiber yam, manufactured by
Bekaert Corporation.
[0042] The term "metal wire" shall mean at least one continuous
metal strand having a diameter greater than the individual metal
fiber/filament described above. The metal wire may contain at least
one or a combination of the following metals: copper, iron,
chromium, nickel, silver, tin, aluminum, gold or other metals
appropriate for the purpose of this invention. The metal wire may
be in the form of solid or stranded wire or thin wire, wound around
a nonconductive fiber core.
[0043] The term "electrically conductive textile fibers" described
in this invention shall mean textile threads/fibers or filaments,
comprising electrically conductive materials. Electrically
conductive textile threads or fibers may be made completely of
electrically conductive fibers, such as metal fibers or
carbon/graphite containing fibers. The carbon/graphite containing
fibers described in this invention shall mean textile fibers,
comprising at least one of the following materials: (a)
carbon/graphite fibers, (b) textile fibers, which contain carbon or
graphite particles inside the polymer fibers, or (c) synthetic
polymer or ceramic fibers coated or impregnated with carbon or
carbon/graphite containing material.
[0044] Electrically conductive textile fibers can contain metal
coated threads or fibers. Such fibers are coated by at least one of
the following higily electrically conductive metals: silver, gold,
aluminum, copper, tin, nickel, zinc, palladium, their alloys or
multi-layer combination. The metal coating may be applied on
carbon/graphite threads, extruded polymer filaments, synthetic
threads/fibers, fiberglass or ceramic threads/fibers by sputtering,
electroplating, electroless deposition or by any other appropriate
metal coating or impregnation technique.
[0045] Electrically conductive textile fibers may be comprised of
nonconductive fibers or particles combined with electrically
conductive fibers, particles or layers of electrically conductive
coating.
[0046] The term "melting fuse" or "fuse" described in this
invention shall mean electrically conductive textile fibers which
melt at the temperatures between 110.degree. C. and 350.degree. C.
Such melting results in termination of the electrical continuity in
said electrically conductive textile fibers.
[0047] The term "sensing means" described in this invention shall
mean at least one of the following materials, which provide
temperature sensing in the heater: (a) electrically conductive
textile fiber, (b) metal wire, (c) electrically conductive polymer,
or other electrically conductive materials. The sensing means is
usually disposed in close proximity to the heating means and
provides temperature sensing by: (a) a change in electrical
resistance of the electrically conductive textile fibers, polymers
or wires due to a temperature change in the heater (such as PTC
temperature sensing means) or (b) transferring electrical signal
from another temperature sensing layer (such as an NTC sensing
layer).
[0048] The sensing means is always connected to an electronic or
electromechanical controller, which varies or terminates electrical
power supply to the heater. The sensing means may be electrically
connected to another heat sensing material such as an NTC sensing
means. The sensing means may have NTC or PTC properties, depending
on the heating element design. As an example, carbon fibers may be
used as NTC sensors and Nickel wire or its alloys may be used as
PTC sensors for sensing means. The sensing means may be
encapsulated by a nonconductive material or it may be free of any
insulation.
[0049] The term "PTC temperature sensing means" described in this
invention shall mean sensing means which possesses positive
temperature coefficient (PTC) properties. It is preferable that the
PTC temperature sensing means has a high resistance value and a
steady linear increase of resistance upon increase of the ambient
temperature.
[0050] The term "current leakage conductor" or "heating element
current leakage conductor" described in this invention shall mean a
highly electrically conductive material which is connected with:
(a) grounding (earth) conductor of the housing/industrial
electrical supply system, or (b) one of the current supply lead
wires (live or neutral) of the controller. It is preferable that
current leakage conductor has a form of either metal mesh or foil,
or continuous bare wire, electrically conductive fabric, or
combination thereof. It can also comprise conductive polymer,
carbon or electrically conductive ceramic fibers. The current
leakage conductor can be wrapped or wound around the heating cable,
or it can be attached to the heating cable as a highly conductive
hot spot detection metal or fabric sheet in case of a flat heater
construction.
[0051] The term "hot spot" or "local overheating area" described in
this invention shall mean the portion of the heater, where the
temperature of NTC sensing means is raised above 60.degree. C.
during operation of the heater, causing significant reduction of
electrical resistance in the portion of said NTC sensing means.
[0052] The term "current leakage limiting setting" described in
this invention shall mean the maximum allowable current value
defined in the controller, at which its electrical or
electromechanical circuit terminates the electrical continuity in
the heater. Usually, the hot spot current leakage limiting setting
is either lower or identical to the current leakage limiting
setting for the mechanical (such as metallic or moisture) intrusion
in the heater.
[0053] The term "mechanical intrusion" or "mechanical damage"
described in this invention shall mean at least one of the
following mechanical problems, which trip (activate) the GFCI or
other current imbalance detection circuits in the controller,
terminating electrical continuity in the heating means: (a) damage
of outer or inner insulation of the heater, (b) mechanical damage
of the conductors and/or heating means (c) moisture penetration
into the heating cable, (d) metallic intrusion into the heater,
which results in interconnecting (short circuiting) of the heating
means, and/or optional return conductor, with current leakage
conductor.
[0054] The preferred embodiment of the invention shown in FIG. 1
describes a flooring heating cable, having heating means (5)
covered by NTC sensing layer (4), heating element current leakage
conductors in a form of grounding metal mesh or foil (2) and
multi-stranded bare wires (3), return conductor (6) having
insulation means layer (7), and two layers of insulation means (1)
and (1'), covering the whole heating cable assembly. The heating
means (5) and return conductor (6) are connected to each other at
one end of the heating cable. As stated above, the return conductor
is also considered a heating means, which can either radiate heat,
or deliver the current from line to neutral terminals of the
heating cable. The important feature of the return conductor is
that it provides cancellation of electromagnetic field in the
heating cable. The NTC sensing means (4) and current leakage
conductors have good mechanical and electrical connection between
each other. In the event of local overheating (usually above
60.degree. C.) of the heating means, the NTC layer becomes more
conductive in the hot spot area, providing a current leakage path
from the heating means (5) to the heating element current leakage
conductors (2) and (3), which can be detected by the GFCI or
another current leakage detecting circuit of the controller.
[0055] FIG. 2 and FIG. 3 demonstrate additional examples of the
heating cable construction. FIG. 2 shows heating means (5),
insulated by NTC sensing layer (4), and insulated return electrode
(6) covered by the current leakage conductor (2) in the form of
mesh or foil shield. The heating means may comprise a strengthening
core made of nonconductive means, metal wires and/or electrically
conductive textile fibers. The inclusion of electrically conductive
textile fibers in the heating means allows manufacturing the
heaters with better flexibility, lower weight and better electrical
redundancy in the event of breaking of some of the conductors
inside the heating means. In addition, the electrically conductive
textile fibers have heat radiating surface areas larger than the
same of resistance metal wires. The larger surface area of the
electrically conductive textile fibers results in a lower
temperature surface density, which reduces thermal
deterioration/aging of the plastic insulation. The electrically
conductive textile fibers may be in the form of carbon or metal
fibers, which can withstand high operating temperatures or they may
be in the form of coated or impregnated synthetic fibers with low
melting temperatures. Such low melting temperature electrically
conductive textile fibers may act as a melting fuse, terminating
electrical continuity in the event of local overheating of the
heating cable. The ability to fuse the conductor in the heating
means makes the heater more reliable, especially in the event of
malfunctioning of the controller.
[0056] FIG. 3 demonstrates an example of a heating cable without a
return conductor. The current leakage conductor (2) is in the form
of metal mesh or foil sheath, which covers the NTC sensing means
(4). Alternatively, metal wires and/or electrically conductive
textile fibers, or combination thereof, can be provided as a
current leakage conductor instead of metal mesh/foil cover sheath
(2). The optional second insulation means (1') covers the heating
element assembly to provide additional mechanical protection.
[0057] FIG. 4A and FIG. 4B show the temperature sensing heating
cable with an optional sensing means. The preferred embodiment
shows a PTC temperature sensing means (8), covered with insulation
(7). The PTC temperature sensing means is usually connected to a
separate electrical circuit of the electronic controller to detect
an average temperature in the heating cable. The current leakage
conductor may be in different forms and materials such as a metal
sheath (mesh or foil) covering (2) shown in FIG. 4A, or metal
wire/electrically conductive textile fiber conductor (3) shown in
FIG. 4B or combination thereof. The current leakage conductor
itself may have at least one of the following functions: (a)
providing a path for current leakage through NTC layer, hence hot
spot detection, (b) providing a radio frequency shield especially
if the metallic foil or mesh is utilized, (c) providing a detection
path for metallic intrusion into the element assembly and (d)
providing a detection path for earth leakage.
[0058] FIG. 5 shows a principal electrical circuit diagram of the
electronic control system and the heating cable with single ended
connection for under floor heating. The heater includes floor
heating cable and an electronic controller with varied power ratio
settings. The heating means (5), which is joined at the far end of
the element assembly to the return conductor (6), is separated from
the outer current leakage conductor (2) by a layer of NTC sensing
means (4). This material is usually in the form of, but not
restricted to, doped Nylon, PVC, Polyethylene or other traditional
insulation polymers.
[0059] As the temperature of the NTC layer rises in the local
overheating area, the resistance falls. This effect usually becomes
apparent at around 60-70.degree. C. degrees, with an almost
exponential response above this level. Any hot spot anywhere along
the length of such heating cable assembly will result in current
leakage to earth via the heating element current leakage
conductor.
[0060] The electronic controller detects a hot spot by comparing
the current flowing in the live connection (shown as "L") of the
heating element with the current flowing in the return wire to
neutral connection (shown as "N"). The comparison is made through
current detectors (9) and (10) and comparator logic device (11).
Any current imbalance is due to a leakage, via the NTC sensing
layer, to earth via the heating element current leakage conductors.
Such current imbalance detection is similar to the manner in which
a regular ELCB (GFCI) works. The novelty of the preferred
embodiment of the invention is not just the means (ground leakage)
of detection, but the fact that the same current leakage detector
can be used for hot spot detection as well as normal earth fault
detection and metallic intrusion detection. This system also
dispenses with the need for a separate sensor wire to detect the
NTC leakage and send a signal to the controller.
[0061] The NTC hot spot detector circuit can take many forms,
ranging from a dual counter wound toroidal transformer with a
detector winding, to the simplified electronic type seen in FIG.
5.
[0062] The electronic controller's current detectors measures the
volt drop across shunt resistors, amplifies and feeds the resultant
voltages to a simple comparator circuit, which in turn disables the
power control circuit if the differential was above a predetermined
level. There are three distinct levels of detection by the
electronic controller. The first level is hot spot detection, the
second (higher) level is earth leakage due to mechanical intrusion
such as element damage/moisture intrusion, and the third level is
direct contact between the heater and the heating element current
leakage conductor caused by metallic penetration into the heating
cable. It is preferable that the current leakage limiting setting
will range from 0.1 mA to 100 mA. It is also preferable to have
different current leakage limiting settings for hot spot detection
and mechanical intrusion. In the event the current leakage limiting
settings for the hot spot is lower than the regular GFCI protection
setting for mechanical intrusion, then it is possible to maintain
the heater in operating condition even if the heating cable has
reached the maximum hot spot temperature level. In that case it is
preferable to have electronics, which will turn the system "ON" and
"OFF" periodically, preventing the heating cable from overheating.
It is also preferable to have a visual and/or sound indicator on
the controller, which will warn the user about the hot spot
occurrence.
[0063] The controller is equipped with power control (12), optional
user selectable power ratio (15), optional room or floor
thermostats (14) and an optional overheat (hot spot) indicator
(13). The heating cable may have an optional PTC temperature
sensing means (8) connected to heating means (5) and return
electrode (6) in one junction (17). The signal from PTC temperature
sensing means (8) transfers to a separate optional PTC detector
(16), which is connected with the main power control (12) of the
electronic controller. The insulation means (1) covers the heating
cable components.
[0064] FIG. 6 shows another preferred embodiment of principal
electrical circuit diagram of the flooring electronic control
system and the flooring heating cable with double ended connection.
The main difference between this diagram and the diagram shown in
FIG. 5 is that the heating cable does not have the return
conductor. The following components are only optional in the
heater: (a) PTC temperature sensing means (8), (b) PTC detector
(16), (c) room or floor thermostats (14) (d) overheat (hot spot)
indicator (13) and (e) user selectable power ratio (15).
[0065] FIG. 7 demonstrates another application 5 of the invention,
where the heater is assembled in flat panel constructions which can
be used as: (a) a heating pad (b) a panel heater for mirror
defogging, (b) a space heater, etc. The proposed flat heater also
consists of heating means (5), encapsulated by NTC sensing means
(4) which is attached to the current leakage conductor (2). The
grounding conductor is attached to the heating cable as a flat
metal foil sheet. The whole flat assembly is insulated by the
optional insulation means (1). It is possible, for the purposes of
this invention, not to use any outer insulation means, or to place
insulation means only on one side of the heater.
[0066] It is preferable to attach metal foil (or conductive fabric
sheet) on both sides of the heating cable to provide better
electrical contact of the NTC sensing layer to the current leakage
conductor. However, the flat metal foil/fabric sheet can be applied
only from one side of the heating cables if dictated by the heating
element design.
[0067] The flat panel heater can be solid or flexible. It can have
different shapes, such as square, rectangular, round or curved. The
heater proposed in this invention also can have a shape of a
continuous flat strip, sleeve or other shapes appropriate for the
purposes of invention, as long as the heater's construction
provides a reliable electrical and mechanical connection between
the following layers: heating means, NTC sensing means and the
current leakage conductor. The proposed heating cable may also have
a shape of a flat cable, sheet or sleeve, laminated or extruded
into the NTC sensing layer.
[0068] The FIG. 8 shows an example of a heating pad with hot spot
detection. The heating cable (17) is placed on the metal foil sheet
(2). The ends of the heating cable are terminated to the live (21)
and neutral (20) current supply conductors, attached to the
electronic controller (18). The sheet type current leakage
conductor (2) is terminated to the cord (22) which is connected to
the controller. The whole pad is pouched by PVC insulation, which
hermetically seals the whole heating construction. The power cord,
having plug (19) with optional ground pin is attached to the
controller.
[0069] In the event the hot spot (23) occurs inside of the heating
pad, the heating cable will leak the current through the NTC
sensing layer to the hot spot detection foil conductor (2), which
trips the protection system of the controller (for example, GFCI),
terminating electrical continuity in the heating pad.
[0070] The same hot spot detection method can be used without
reference to actual Earth (or Ground). For example, the electrical
blanket (or mattress pad) heating cable (24), shown in FIG. 9, may
comprise outer insulation means (1), heating means (5) covered by
NTC sensing means (4) and current leakage conductor (2). The
current leakage conductor is electrically connected either to the
ground circuit, or to one of the current supply (live or neutral)
conductors/lead wires. Alternatively, the NTC sensing means can
cover not the heating means (5), as shown on FIG. 9, but the
current leakage conductor (2). NTC sensing means can also insulate
both: heating means (5), and current leakage conductor (2).
[0071] FIG. 10A and FIG. 10B show the preferred embodiment of
principal electrical circuit diagram of the electrical heating
blanket with hot spot detection, which does not require connection
to the ground. FIG. 10A demonstrates the heating cable comprising
insulation means (1), heating means (5) and current leakage
conductor (2), which is separated from heating means by NTC sensing
means (4). The current leakage conductor (2) is connected to the
live current supply conductor/lead wire ("L"), which feeds the
power to the controller, at a junction (25). In the event of a hot
spot occurrence, the current leaking through NTC layer (4) between
heating means (5) and current leakage conductor (2), is detected by
current detectors (9) and (10). The current imbalance is measured
by a leakage comparator logic (11) which sends a signal to the
controller's regulation system.
[0072] FIG. 10B shows the same principal electrical circuit as
shown on FIG. 10B, with the difference that the current leakage
conductor (2) is connected to neutral ("N") current supply
conductor of the controller (instead of live current supply
conductor) at ajunction (25). No grounding of current leakage
conductor is required in the heater to detect the hot spot by the
current leakage imbalance method according to this preferred
embodiment of the invention.
[0073] The process of manufacturing the temperature sensing heating
cables and their assembly in the heating products can be fully
automated. Some designs of the heaters may be manufactured in rolls
or spools with subsequent cutting to predetermined shapes and
sizes.
[0074] Further, the proposed heaters can be utilized in, but not
limited to: (a) electrically heated blankets, throws, pads,
mattresses, pet beds, space heating panels, foot warmers, mats,
bedspreads and carpets; (b) electrically heated walls, ceiling and
floor electric heaters; sub flooring, office dividers/panels,
window blinds, roller shades, mirrors, fan blades and furniture
heaters; (c) refrigerator, road, driveway, walkway, window, roof,
gutters and aircraft/helicopter wing/blade deicing systems, (d)
pipe line, drum and tank electrical heaters, (e) medical/health
care, (f) electrically heated food bags or food storage, sleeping
bags, towels, boot and glove dryers, etc.
[0075] The aforementioned description comprises different
embodiments, which should not be construed as limiting the scope of
the invention but as merely providing illustrations of some of the
presently preferred embodiments of the invention.
[0076] While the foregoing invention has been shown and described
with reference to a number of preferred embodiments, it will be
understood by those possessing skill in the art that various
changes and modifications may be made without departing from the
spirit and scope of the invention.
* * * * *